If a character turns into a dragon, their relationships would change drastically. For example, if it was a knight who had many friends among the other knights, they would be seen as a threat once they start to transform. Their former friends might try to hunt them down out of fear. On the other hand, if it was a character who was previously an outcast, like a bastard, their new form could give them power and respect. They could form new alliances with those who seek to use a dragon's power for their own gain.
His relationship with his uncle Iroh would be deeply affected. Iroh has always been a guiding figure for Zuko. If Zuko turns into a dragon, Iroh would be worried but also proud in a way. He would search for ways to help Zuko, and their relationship would become more about Iroh protecting and guiding Zuko in this new and strange form. Zuko, in turn, would rely more on his uncle's wisdom during this time.
In a fanfiction where Issei turns into a dragon, his relationships would be in flux. His relationship with his mentors or those he looks up to might change as they now see him as a different kind of being. They might treat him with more caution or more respect depending on how they view dragons. His friendships with his peers would also be altered. Some might see him as a weapon to be used in their battles or struggles, while others would see him as a friend in need of support. Romantically, if he had feelings for someone, that person would have to deal with the fact that Issei is no longer fully human. There could be jealousy from others who might want to be with the powerful dragon - Issei, or there could be newfound admiration from those who previously overlooked him.
With his human friends, it would be really tough. They might be scared of him at first. Astrid, for example, would be conflicted. She was attracted to Hiccup as a human, but now he's a dragon. She would have to overcome her fear and try to find a way to communicate with him. And Hiccup would feel isolated from his human friends, longing for the connection they once had.
For Naruto, he might become more protective of Sasuke as a girl. Their friendship could take on a different dynamic, with Naruto being more chivalrous perhaps. Sakura might initially be jealous but then they could form a stronger bond as girls sharing common experiences. Kakashi would probably have to adjust his mentoring style to account for Sasuke's new situation.
His friends would be both amazed and a bit scared at first. Hermione would immediately start researching ways to turn him back. Ron might be more in awe of Harry's new form, but also worried about how dangerous it could be. Their dynamic would shift as they now have to protect Harry in a different way. They might also have to hide his transformation from others who could misunderstand and try to harm Harry.
If Eragon turns into a dragon, his relationship with Saphira would be very different. They might become equals rather than dragon and rider. His human friends may be initially scared or confused. But some, like Arya, might see it as an opportunity to gain a powerful ally for the fight against evil. His enemies would be more fearful of him, seeing him as a greater threat.
Romantically, she would have different options. Instead of being with Harry Potter, she could be involved with a Westerosi nobleman or a powerful warrior. Their relationship would be shaped by the power dynamics and political intrigues of Game of Thrones. It would be less about pure love and more about alliances and survival. For instance, she might be forced to marry someone she doesn't love at first to secure her family's position.
His relationship with Toothless would be very different. Toothless might be initially confused and a bit hesitant around Hiccup in his new form. But as time passes, they would develop a new kind of bond based on Hiccup having to adapt to being a dragon. With Astrid, it could be strange at first. Astrid might be both curious and a bit jealous of Hiccup's new dragon form. She would have to see Hiccup in a whole new light.
It would make her more confident. Having a dragon gives her a huge power advantage, and she would no longer have to rely solely on her assassin skills. This newfound power could make her bolder in her actions and decisions.
It would likely make her more powerful and feared. Having a dragon gives her a huge advantage in battles and in political power plays. Her character might become more confident and assertive, as she now has a great weapon at her disposal. She could use the dragon to exact revenge on her enemies more swiftly and decisively.